Around 35 million years ago, a rift valley of about 300 km long and 50 km wide came into being between the present cities of Basel and Frankfurt. This was due to tensile stresses in the Earth's crust and mantle, which resulted in lowering the earth's surface. The moat has been partially filled up again by sedimentation. On the edges we find mountain ridges, the so-called "rift flanks". On the Eastern side, they are the Black Forest and Odenwald mountains, in the West the Vosges and Palatinate Forest. During the tertiary, the High Rhine continued West from Basel and flowed via the Doubs and the Saône, into the Rhône. The rift diverted the Rhine into the newly formed Upper Rhine Valley.

The Rhine knee at Basel marks the transition from the High Rhine to the Upper Rhine with a change of direction from West to North and a change of landscape from the relatively small-chamber high-Rhine cuesta landscape to the wide rift zone of the Upper Rhine Rift Valley. The two largest tributaries come from the right: the Neckar in Mannheim, the Main across from Mainz. In the northwest corner of the Upper Rhine Valley, at Rhine-kilometer 529.1, near Bingen, where the Nahe flows into the Rhine, the Rhine flows into a gorge in the Rhenish Massif and thereby changes into the Middle Rhine.[1]

In 1685, Louis XIV started a program to move the Upper Rhine, change its course and drain the flood plain, in order to gain land. Until 1840, the river was moved up to 1.5 km to the East, taking territory away from Baden. Around 1790, large part of the Rhine Valley were deforested, creating arable land, fields and pasture to feed the population. The Upper Rhine was straightened between 1817 and 1876 by Johann Gottfried Tulla and changed from a relatively sluggish meandering river with major and many smaller branches into a fast flowing stream flanked with dams. The length of the Upper Rhine was reduced by 81 km. Some cut-off river arms remain; they are typically called "Old Rhine" (German: Altrhein) or Gießen.

The Rhine between Basel and Iffezheim is almost entirely canalized. On a stretch of 180 km, there are ten dams, provided with hydropower station and locks. Between Basel and Breisach, the old river bed carries hardly any water; almost all water is diverted through the Grand Canal d'Alsace on the French side, to ensure safe shipping and hydro power generation around the clock. Only when there is a large supply of water, then the old river bed will receive more water than the canal. France gained the right to do this in the 1919 Treaty of Versailles; the right applies to the segment between Basel and Neuburgweier/Lauterbourg, where the Rhine forms the border between France and Germany.

Weir at Breisach; to the left a lock; to the right a small power station under construction

The straightening (1817-1876) and channeling (1928-1977) reduced the water table by up to 16 m and thus had a negative effect on flora and fauna. Gravel is also missing from the river, due to the dams. This has caused erosion below the dam at Iffezheim. To counter this, 173.000 cubic meters per year of a mixture of sand and gravel with an average grain diameter of 20 mm (corresponding to the local sediment transport capacity) has been dumped into the river, since 1978, using two motorized barges.

The Upper Rhine plays a key role in flood control on the Middle and Lower Rhine. As a result 0f the straightening of the Upper Rhine, floods from the Alps now reach the Middle Rhine much faster than in the past. Thus, the risk of such a peak coinciding with a flood peak of Neckar, Moselle or Main has increased. About 123 km² of flood plain have been lost. Authorities in riparian states of France, Baden-Württemberg and Rhineland-Palatinate have launched the Integrated Rhine Programme, a framework for designating water retention areas. to combat downstream flooding. A French-German treaty was concluded in 1982, in which the parties agreed to restore the retention capacity on the stretch below Iffezheim to the level it had before the area was developed.

This means: For the stretch between Iffezheim and the mouth of the Neckar, attenuation of the apex of a 200-year flood (i.e. a flood that statistically occurs once in 200 years) of the Rhine to a discharge of 5000 m³/s at the Maxau gauge station, that is, a reduction from 5700 m³/s to 5000 m³/s.

for the stretch below the mouth of the Neckar, attenuation of the apex of a 220-year flood to a discharge of 6000 m³/s at the Worms gauge station, that is, a reduction from 6800 m³/s to 6000 m³/s.

For this purpose the following measures are planned and partially implemented:

By France: Special operations power stations on the Rhine and construction of two polders Erstein and Moder

By Baden-Württemberg: Construction of about 13 polders

By Rhineland-Palatinate: construction of polders and relocating levees

The effectiveness of the flood protection measures was verified using a computer model. The State Institute for the Environment, Nature Protection and Measurements in Baden-Württemberg carried out forecast calculations with the help of a mathematical "synoptic flood progression model". The analysis of the calculations and the evaluation of the results were made on the basis of the requirements and methods set by the international Flood Study Commission for the Rhine. The implementation of the proposed flood control measures on the Upper Rhine can prevent the occurrence of a 200-year flood between Iffezheim and Bingen, with an overall economic loss estimated at around 6.2 billion euros.

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Do not translate text that appears unreliable or low-quality. If possible, verify the text with references provided in the foreign-language article.

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The Upper Rhine tri-national region (French: Région Métropolitaine Trinationale du Rhin Supérieur, German: Trinationale Metropolregion Oberrhein) is a Euroregion that covers the border areas of the Upper Rhine (the northern part of the Upper Rhine valley and the Palatinate are not included as they are not border areas) and parts of the High Rhine. As the name suggests, it is a tri-national region comprising parts of France, Germany and Switzerland. The regional Upper Rhine Conference is a framework for future political and administrative cooperation in the area.